Production method of foamed electric wire

Abstract

The present invention discloses a production method of a foamed electric wire, whereby a foamed electric wire is obtained via a foamed insulation layer formation step of forming a foamed insulation layer on a conductor, wherein the foamed insulation layer formation step includes: a step of introducing a base resin into an extruding machine, a step of introducing a foaming agent into the extruding machine, and a step of extruding a mixture containing the base resin and the foaming agent from the extruding machine and forming the foamed insulation layer on the conductor, and wherein the resin contained in the mixture has a shear stress of 0.40 to 0.80 Mpa, and the base resin is a propylene-based resin.

The invention claimed is: 
     
       1. A production method of a foamed electric wire, whereby a foamed electric wire is obtained via a foamed insulation layer formation step of forming a foamed insulation layer on a conductor, wherein
 the foamed insulation layer formation step includes: 
 a step of heating pellets of a raw material propylene-based resin at a temperature of 200° C. to less than 270° C. to form a melt; 
 a step of, after forming the melt and before mixing with a foaming agent, reforming pellets from the melt to produce base resin pellets having a shear stress of 0.40 to 0.80 MPa, 
 a step of introducing the base resin pellets into an extruding machine, 
 a step of introducing the foaming agent into the extruding machine, 
 a step of kneading a mixture containing the base resin pellets and the foaming agent, and 
 a step of extruding the mixture from the extruding machine and forming the foamed insulation layer on the conductor. 
 
     
     
       2. The production method of a foamed electric wire according to  claim 1 , wherein the propylene-based resin is an ethylene-propylene-based copolymer. 
     
     
       3. The production method of a foamed electric wire according to  claim 1 , wherein the melt tension at break of the resin contained in the mixture is 15 mN or more. 
     
     
       4. The production method of a foamed electric wire according to  claim 1 , wherein the mixture containing the base resin pellets and the foaming agent is kneaded at a temperature of 170 to 200° C. before extruding the mixture from the extruding machine. 
     
     
       5. The production method of a foamed electric wire according to  claim 3 , wherein the propylene-based resin is an ethylene-propylene-based copolymer.